The present invention relates to a carbon dioxide fire extinguishing device.
For fire extinguishing devices with gaseous extinguishing media it is prescribed that the pressure vessel in which the extinguishing medium is stored under pressure is checked for gas losses. In the case of carbon dioxide pressure cylinders, it must be ensured that a gas loss of over 10% of the filling weight is reliably detected. In their periodic testing, transportable carbon dioxide fire extinguishers are weighed by means of a calibrated balance. As a result, a gas loss between two tests remains unnoticed. In the case of stationary carbon dioxide fire extinguishing systems, the carbon dioxide pressure cylinders hang individually in a weighing device, so that the weight of each individual carbon dioxide pressure cylinder is continuously monitored. If the weight falls below a fixed weight, an alarm is set off. Such weighing devices for suspending carbon dioxide pressure cylinders significantly increase the cost of stationary fire extinguishing devices. Moreover, they must be calibrated at regular intervals.
Until now, there has been no satisfactory alternative to the weighing of carbon dioxide pressure cylinders.
Pressure monitoring procedures are entirely unsuitable for detecting a gas loss from a carbon dioxide pressure cylinder, since, in the case of a customary filling ratio of 1:1.50 (i.e. a filling weight of 0.666 kg of carbon dioxide per liter of cylinder volume), below a temperature of 27xc2x0 C. a gas loss of 10% no longer causes a significant drop in pressure in the cylinder (in the case of a filling ratio of 1:1.34, i.e. a filling weight of 0.746 kg of carbon dioxide per liter of cylinder volume, this lower temperature limit is even around 22xc2x0 C.). Moreover, the pressure in the carbon dioxide pressure cylinder is highly temperature-dependent.
At least in the case of fire extinguishing devices, filling level gages with floats have also been unable to establish themselves as an alternative to the weighing of carbon dioxide pressure vessels. A valve with an integrated filling level gage with a float, as known for example for a carbon dioxide pressure cylinder from the U.S. Pat. No. 4,580,450, cannot be used in carbon dioxide fire extinguishing systems because the linkage of the filling level gage takes up considerable space in the valve base and this means that the inlet bore for the gas in the valve base has to be relatively small. It should be noted in this connection that carbon dioxide pressure cylinders for stationary carbon dioxide fire extinguishing devices have in the neck of the cylinder an internal thread of only W 28.8xc3x97{fraction (1/14)}xe2x80x3 according to DIN 477. It must be possible to screw into this internal thread a valve base which has a prescribed inlet bore for the extinguishing agent of at least 12 mm in diameter, in order that the carbon dioxide can flow into the valve with a low pressure loss after the fire extinguishing device is put into action.
The U.S. Pat. No. 5,701,932 discloses for gas cylinders with high-purity gases a gas cylinder valve with a built-in capacitive filling level measuring device as an alternative to a mechanical filling level measurement with a float. The capacitive filling level measurement described in U.S. Pat. No. 5,701,932 is based here on the principle that the liquid phase of a gas has a far higher dielectric constant than the gaseous phase, so that dropping of the liquid level in the pressure cylinder is reflected by a reduction in the capacitance of the probe. This measuring principle consequently presupposes that the measurement takes place at a given ambient temperature, at which it is ensured that there are two separate phases in the pressure cylinder, and that the level of the liquid in the pressure cylinder drops if gas is extracted from the pressure cylinder. However, by contrast with the application for high-purity gases described in U.S. Pat. No. 5,701,932, this is by no means always the case with a carbon dioxide pressure cylinder for fire extinguishing purposes. In fact, one application for fire extinguishing devices where carbon dioxide pressure cylinders are used is in machine rooms for protecting equipment, where it is quite possible for ambient temperatures of over 40xc2x0 C. to be reached.
With a filling ratio of the carbon dioxide pressure cylinder of 1:1.50 (i.e. 0.666 kg of carbon dioxide per liter of cylinder volume), the liquid phase of the carbon dioxide then already takes up the entire volume of the cylinder when the temperature reaches 27.2xc2x0 C., so that above this temperature a gas loss no longer necessarily brings about a change in the level of the liquid in the pressure cylinder. Moreover, the critical temperature of the carbon dioxide from which the carbon dioxide forms a supercritical fluid, because there is in any case no longer any difference between a gaseous phase and a liquid phase, is as low as 31xc2x0 C.
Furthermore, it should be noted with respect to the valve with the filling level measuring device from U.S. Pat. No. 5,701,932 that it is also not suitable for flow-related reasons for carbon dioxide pressure cylinders in fire extinguishing devices. In fact, in a valve base with a screw-in thread of W 28.8xc3x97{fraction (1/14)}xe2x80x3, the fitting of the capacitive measuring probe takes up so much space that there is no space left for an inlet bore of at least 12 mm in diameter for the carbon dioxide extinguishing gas. To obtain enough space for such a 12 mm inlet bore in the valve base, the diameter of the capacitive measuring probe could of course be made even smaller. However, for this it would be necessary to accept stability problems with respect to the measuring probe, which cannot be tolerated in the case of an element with relevance to safety.
The present invention is accordingly based on the object of reliably checking the carbon dioxide pressure vessel in a carbon dioxide fire extinguishing device for gas losses without weighing, at both low and high ambient temperatures. This object is achieved according to the invention by a device as claimed in claim 1.
In a carbon dioxide fire extinguishing device according to the invention, a capacitive measuring device which is calibrated for a temperature range above and below the critical temperature of the carbon dioxide is used for detecting a gas loss from the carbon dioxide pressure vessel. In other words, the present invention is based on the surprising realization that a capacitive measuring device can not only measure changes in the liquid level in the pressure vessel in a known way but a measurable change in capacitance can also be unequivocally assigned to a gas loss from the pressure vessel even above the critical temperature of the carbon dioxide, i.e. when there is no longer any physical difference between the gaseous phase and the liquid phase of the carbon dioxide. In this way, a simple solution is provided for detecting a gas loss from a carbon dioxide pressure vessel of a fire extinguishing device which can even be used at high ambient temperatures (i.e. temperatures above 30xc2x0 C.) and makes laborious weighing of the pressure vessel superfluous.
Such a capacitive measuring device preferably comprises a capacitive measuring probe which extends over the entire height of the pressure vessel, a measuring module for measuring the capacitance of the capacitive measuring probe, a microprocessor for processing the measured capacitance values, which assigns to a measured change in capacitance a corresponding gas loss, and also means for generating an alarm message if the gas loss determined by the microprocessor exceeds a given value.
The calibration preferably takes place electronically, using for example a temperature sensor and a memory with calibration values for a temperature range above and below the critical temperature of the carbon dioxide. The microprocessor resorts temperature-dependently to the calibration values in the memory in order to assign to a measured change in capacitance a corresponding gas loss. If the calculated gas loss exceeds a given value, the microprocessor generates an alarm message.
Such a device is outstandingly suitable for checking the gas content of carbon dioxide pressure cylinders, both at high ambient temperatures and at low ambient temperatures. It is accordingly particularly suitable for use in carbon dioxide fire extinguishing devices, in which the ambient temperature may lie between xe2x88x9220xc2x0 C. and +60xc2x0 C.
In order that this device can also be used unproblematically in a carbon dioxide fire extinguishing device in combination with a carbon dioxide pressure cylinder, the present invention has additionally solved the problem of introducing the capacitive measuring probe into the carbon dioxide pressure cylinder through the narrow cylinder neck in such an advantageous way that the outflow resistance of the extinguishing gas from the pressure cylinder is hardly increased at all. For this purpose, the present invention has provided an outlet valve for a carbon dioxide pressure cylinder with an integrated capacitive measuring probe, a first measuring electrode being formed by a rising tube which opens into the valve base and a second measuring electrode being formed by an electrode tube which surrounds the rising tube, with an intermediate gap, over its entire length. This outlet valve has the end effect of providing a simple, reliable and low-cost possible way of checking transportable carbon dioxide fire extinguishers for gas loss more easily and more frequently, and of avoiding complex weighing devices for carbon dioxide pressure cylinders in stationary carbon dioxide fire extinguishing devices. It must be emphasized in particular that such an outlet valve with a measuring probe may have approximately the same outflow resistance as a flow-optimized outlet valve without a measuring probe. At the same time, the capacitive measuring probe, in the case of which the rising tube forms an internal measuring electrode, is distinguished by excellent stability even in the case of large pressure cylinders. Forms of this valve in which the electrical connection to the capacitive measuring probe is solved in a particularly space-saving and trouble-free way are likewise presented.
In the case of a first configuration, an insulating sleeve surrounds the first end of the rising tube in the inlet bore of the valve base and insulates it electrically from the conducting valve base. In the inlet bore of the valve base, this first end of the rising tube is then in electrical contact with a contact element which is electrically insulated from the conducting valve base. The outer electrode tube, on the other hand, is electrically in contact with the conducting valve base and is electrically connected via the latter. The first end of the rising tube advantageously has an annular end face as a contact face for the insulated contact element, so that, to establish a reliable electrical connection between the insulated contact element and the rising tube, the latter merely has to be pressed in the axial direction onto the contact element in the inlet bore of the valve base.
An insulated contact element suitable for this first configuration advantageously comprises a contact ring with approximately the same inside diameter and outside diameter as the annular contact area of the rising tube, and also an insulating ring with a larger outside diameter than the contact ring. This insulating ring rests with one end face against a shoulder face in the inlet bore and has in the other end face a recess into which the contact ring is made to fit. In the case of this configuration, a trouble-free contact of a large surface area is ensured between the rising tube and the contact element, at the same time reliably preventing an electrical short-circuit.
In the case of this first configuration, the valve base advantageously has a connecting channel, which forms an opening in the aforementioned shoulder face, on which the insulating ring rests in the inlet bore. The insulating ring then has for its part an annular groove in the end face, which rests on this shoulder face, the opening of the channel in the shoulder face opening into this annular groove, and a through-bore of the insulating ring extending from the annular groove to the contact ring. In the case of this configuration, an insulated connecting wire is then firmly connected by one end to the contact ring and inserted through the through-bore and the annular groove of the insulating ring into the connecting channel. The annular groove thereby prevents the connecting wire from being sheared off if the contact element is twisted in the inlet bore.
The second end of the aforementioned connecting wire is firmly connected to an externally accessible connecting element, the latter being fitted in a sealed and electrically insulated manner into a bore of the valve base. The conducting valve base establishes an electrical contact with the outer electrode tube. The electrical contact between the outer electrode tube and the valve base can then be established via an annular end face of the outer electrode tube, which is pressed against an annular end face of the valve base.
In the case of this first configuration, one end of the insulating sleeve preferably protrudes out of the bore of the valve base and serves for fastening the outer electrode tube. In an advantageous configuration, this electrode tube is, for example, screwed onto this end of the insulating sleeve in such a way that its annular end face is pressed firmly against the annular end face of the valve base. The insulating sleeve consequently thereby performs the function of an electrical insulator between the rising tube and the valve base, of an insulating spacer between the rising tube and the outer electrode tube and of a fastening and pressing device for the outer electrode tube. As a result of this multi-functional sleeve, a minimum of individual parts are required for the fitting of the two measuring electrodes. The insulating sleeve may, furthermore, have an electrically conducting outer wall, via which the valve base and the outer electrode tube are electrically connected to each other. As a result, the electrical contact between the valve base and the outer electrode tube is further improved.
In an alternative configuration of the measuring electrode, the rising tube is screwed by its upper end into the inlet bore of the valve base. An upper insulating sleeve is pushed onto the upper end of the rising tube. A lower fastening sleeve is screwed onto the lower end of the rising tube, the screwed-on fastening sleeve pressing the outer electrode tube axially against the upper insulating sleeve. The upper insulating sleeve is thereby advantageously pressed against an end face of the valve base. A preferred configuration of the lower fastening sleeve comprises a metallic core body, which is screwed onto the lower end of the rising tube, and an insulator, which is arranged between the metallic core body and the outer electrode tube.